Models and parametrizations of hadro- and photo-
production reactions on nucleons

Mark ParisGeorge Washington University

The non-perturbative regime of QCD is populated by an
array of hadronic resonances. Precisdion data on polarization observables with large
angular coverage from exisitng and planned e.m. facilities have ushered in a
renaissance in reaction theory and light hadron spectroscopy. Baryon resonance production
gives a strong contribution to the reaction cross sections in these experiments. But
non-resonant contributions to the scattering and reaction observables, particularly in
single meson production experiments, generally are not small. This complicates the
extraction of the nucleon resonance spectrum from data. We apply a coupled-channel
dynamical model and the Chew-Mandelstam parametrization approach to gain a better
understanding of the single meson production experiments and what they say about the
nucleon resonance spectrum.